Stereospecific block copolymer

Several different techniques for the preparation of stereospecific block copolymers of styrene and butadiene have been studied using an SEC-RI system [56]. The block copolymers prepared free of impurities showed a single peak, and those prepared in the presence of impurities showed two peaks which were identified by fractionation and IR spectrophotometry. 

Solvents influence the rate of free-radical homopolymerization of acrylic acid and its copolymerization with other monomers. Hydrogen-bonding solvents slow down the reaction rates. Due to the electron-withdrawing nature of the ester groups, acrylic and methacrylic ester polymerize by anionic but not by cationic mechanisms. Lithium alkyls are very effective initiators of a-methyl methacrylate polymerization yielding stereospecific polymers.Isotactic poly(methyl methacrylate) forms in hydrocarbon solvents. Block copolymers of isotactic and syndiotactic poly(methyl methacrylate) form in solvents of medium polarity. Syndiotactic polymers form in polar solvents, like ethylene glycol dimethyl ether, or pyridine. This solvent influence is related to Lewis basicity in the following order ... 

Formation of AC-2 results in a more substantial transformation of bonds than the formation of AC-1. A different spatial structure of AC-2 is formed, which has the flower shape and permits both mono and bidentate coordination of 1,3-dienes, as well as putting less restrictions on their coordination with a monomer for all the positions of substituent at the C = C bond, in relation to a crystal surface. This is the reason for AC-2 stereospecificity and the aforementioned possibility of stereo block copolymer formation during a-polymerisation in the presence of Ziegler-Natta catalytic systems. AC-2 can orient unsaturated C = C bonds of 1,3-dienes to bidentate coordination on the bidentate AC. 

In these two decades remarkable progress has been made in the development of excellent catalysts for living and stereospecific acetylene polymerizations (10,26-28). The r-conjugated polymers prepared by the sequential polsrmerization are strictly limited to polyacetylenes, except for only a few examples. Thus, synthesis of tailor-made conjugated macromolecules such as end-functionalized polymers, block copolymers, star-shaped polymers is possible only in the case of substituted acetylenes. 

Living radical polymerization (atom transfer radical pol5mierization) has been developed which allows for the controlled polymerization of acrylonitrile and comonomers to produce well defined linear homopolymer, statistical copolymers, block copolymers, and gradient copolymers (214-217). Well-defined diblock copolymers with a polystyrene and an acrylonitrile-styrene (or isoprene) copolymer sequence have been prepared (218,219). The stereospecific acrylonitrile polymers are made by solid-state urea clathrate polymerization (220) and organometallic compounds of alkali and alkaline-earth metals initiated polymerization (221). 

Incoronata Tritto studied stereospecific olefin polymerization in the group of Prof. Adolfo Zambelli at the Institute for Macromolecular Chemistry of the CNR and received her degree in polymer science at the Specialization School Giulio Natta at Politecnico di Milan (Italy) in 1981. In 1982, she joined as permanent researcher the Institute for Macromolecular Chemistry of the CNR In 1988, she spent 1 year in the group of Prof. Robert H. Grubbs at Caltech (USA), where she studied the relationship between metathesis and addition olefin polymerization. She is currently a senior research chemist at ISMAC-CNR. Her research interests focus on (1) synthesis and microstmctural characterization of stereospecific olefin and cyclic olefin homo- and copolymers by transition metal catalysts (2) activation and deactivation reactions ofthe homogeneous catalytic systems by in situ multinuclearNMR analysis and (3) synthesis of block copolymers and nanostructured hybrid polymers, in situ polymerization on clay and carbon nanotubes. 

The method is used for the preparation of Block Copolymers or Stereospecific polymers. 

Synthetic polymers in general can be classified (1) by thermal behavior, i.e., thermoplastic and thermosetting (2) by chemical nature, i.e., amino, alkyd, acrylic, vinyl, phenolic, cellulosic, epoxy, urethane, siloxane, etc. and (3) by molecular structure, i.e., atactic, stereospecific, linear, cross-linked, block, graft, ladder, etc. Copolymers are products made by combining two or more polymers in one reaction (styrene-butadiene). See cross-linking block polymer epitaxy homopolymer plastics. 

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